The Multilateral Initiative in Malaria, an international collaborative research and development program, was established in an attempt to control one of the most significant infectious diseases in the world. One goal of this program is to develop a multivalent, multistage, subunit vaccine against Plasmodium falciparum, the protozoan responsible for the majority of severe malaria and death. A major focus is on the selection of the most effective antigen combinations, adjuvants and delivery systems for immunization. The overall goal of this project is to evaluate and optimize the use of a combination of two blood-stage malarial antigens to induce immunity against challenge infection. Immunization studies will utilize immunologically intact mice as well as gene targeted knockout mice deficient in the expression of antibody mediated immunity (AMI) or cell mediated immunity (CMI) against the murine malarial parasite, Plasmodium chabaudi. The hypothesis to be tested is that enhanced protection against malaria can be achieved by immunization with combinations of blood-stage antigens that activate both AMI and CMI. Immunization will utilize P. chabaudi apical membrane antigen-1 and merozoite surface protein-1, homologues of P. falciparum antigens currently being considered for the immunization of human subjects. Immunologically intact mice will be immunized with individual recombinant antigens in selected adjuvants or with DNA vaccine constructs to establish the protective capacity of each antigen. For protective responses induced, the contribution of AMI and/or CMI will be defined using established immunologic knockout models. Based on the knowledge gained, combinations of defined antigen vaccines will be formulated and tested for the ability to enhance overall efficacy. Measurable immune parameters which correlate with protective T cell and B cell responses induced by combined vaccine formulations will be defined using the knockout models and tested in intact mice. The results obtained will provide a solid experimental basis for P. falciparum vaccine trials in humans.